To protect a wind turbine blade from lightning strikes, normally, a receptor (metal lightning-receiving part) is mounted to a blade surface to receive lightning strikes. A receptor is, for instance, connected to an earth wire via a down-conductor so as to guide lightning current received by the receptor to the earth wire.
For instance, Patent Document 1 discloses a wind turbine power generating apparatus including a plurality of receptors disposed on the surface of a blade body so as to be exposed, and a down-conductor disposed inside the blade body and connected electrically to the receptors.